Method of strengthening structural members under load



A. G. LEAKE- July 22, 1930.

METHOD OF STRENGTHENING STRUCTURAL MEMBERS UNDER LOAD Z Sheets-Sheet 1Filed May 17, 1929 A. G. LEAKE 1,770,933

METHOD OF STRENGTHENING STRUCTURAL MEMBERS UNDER LOAD July 22, 1930.

Filed May 1'7, 1929 2 Sheets-Sheet 2 due/snags Patented July 22,1930

PATENT OFFICE ARTHUR G. LEAKE, OF BBIDGEPORT, CONNECTICUT METHOD ESTRENGTHENING sTnUcTUnAL MEMBEEs UNDER Loan Application filed May 17,1929. Serial No. 863,867.

This invention relates to a method of strengthening structural memberssuch as beams, girders, columns and the like while they are under load,and has for an object to 6. rovide a method of strengthening suchmemtaken substantially on line 1818 of Fi 14.

ers which will not require tearing down the structures, so that the workmay be accomplished in much shorter time and at much less expense andwith a minimum interference with traflic or use of the structure. Thisapplication relates more particularly to the method described in mycopending application Serial No. 363,866, filed May 17, 1929, as moreparticularly adapted for reenforcing or strengthening members undercompression. Diflerent uses of, this method are illustrated in theaccompanying drawings in which Fig. 1 is a top plan view of a girderbuilt up of plate and angle bar construction with a strengthening bar inplace for the first op- Y oration.

Fig. 2 is a side elevation thereof. Fig. 3 is a side elevation showingsubsequent steps of the operation.

Fig. 4 is a similar view showing still further steps. 7

Fig. 5 is a side elevation on an enlarged scale of one end of thegirder.

Fig.6 is a top plan view thereof. Fi 7 is a detail section substantiallyon line i --7 of Fig. 4. v

Fig. 8 is'a perspective view of an angle bar showing how my improvedmethod of strengthening may be used in connection therewith. g 4

Figs. 9 and 10 are perspective views showing how it may be employed inconnection with channel bars. 4 Fig. 11 is a sideelevation of an uprightcolumn with which my improved method may be employed. 4

Fig. 12 is a similar view showing the first step in the method ofstrengthening this column.

step.

Fig. 14 is a similar view showing the final step.

Fig. 15 is a view looking from the right of Fig. 14.

Fig. 13 is a similar view showing the next Fig. 16 is an enlarged Viewof the upper portion of Fig. 15. V

Fig. 17 is a partial section substantially-on line 17-17 of Fig. 16, andv Fig. 18 is a section on an enlarged scale As indicated above thedrawings an description of this application are directed moreparticularly to strengthening beams and columns which are undercompressionwhen un- 00 der load, and to the method of strengtheningthese members while they are under load.

Referring first to Figs. 1 to? inclusive the girder is composed of theplate 19 with the angle bars 20' and 21 riveted to the upper and 06lower edges thereof respectively. 'It will be understood that the bars20 are under compression. The strengthening member is shown as a rolledsteel. plate 22 of desired length, width and thickness. The firstoperation is to weld one end to the flan cs 23 of the bar 20 asindicated at 24. As t e bar is to be under compression itis contractedor shortened to place it under initial stress. This may be done bycooling it direct with any suitable agent such as liquid carbon dioxide(CO or other suitable cooling agent. It is preferred however, to firstbuckle out the cen-- tral portion of the plate away from the flanges 23forcing it out by suitable means such as wedges or jacks, a wedge beingshown at 24. This shortens the effective length of the plate. Gaugemarks may be provided to indicate how much the plate is to be shortenedto secure the required initial stress as will be determined bycomputation. These are shown at 25, Figs. 2 and 3. -As shown in Fig. 3,the wedge 24 has decreased the eflective length of the plate 22 asindicated at 25. The free end of this plate or that is the end oppositeto the weld 24 is now welded to the flanges 23 as indicated at 26. Thewed e or the forcing means 24 are now remove and the plate is chilled byany suitable means such as carbon dioxide until the plate contracts soas to lie against the flanges 23 throughout its entire length. The plateis then clamped to the flanges by any suitable means such as theremovable clamps 27 These clamps retain the plate tightly against theflanges and retain it in this position while the plate returns to normaltemperature or that 18 sub to which the plate was contracted. After theplate has gained its original temperature it is welded to the flanges atpoints between the two end welds, preferably by tack welds 28, which arewelds of about one-half to two inches long. The clamps 27 may then beremoved and the operation is complete. As the strengthening member isunder initial stress it immediately assumes its part of the load, and bythis method the initial stress is placed in the reenforcing memberwithout the neces sity of jacking up the structure with the consequenthigh cost.

In Fig. 8 is shown how this method can be employed for strengthening anangle bar. The strengthening plates 29 are appliedto the flanges or thebar 30 in the same manner as described above.

Figs. 9 and 10 illustrate how the method may be employed forstrengthening either the flanges 31 or the web 32 of channel bars. Withthis type of bar the strengthening plates 33 and 34 are applied to theflanges or. to the web respectively in the same manner as describedabove.

In Figs. 11 to 18 I have shown how the method may be employed forstrengthening or reenforcing upright columns. These columns may be ofvarious cross-sections but are illustrated as being I -beam columns 35supported on suitable foundations 36. In reenforcing these columns whileunder load two reenforcing plates are used, one for the face of each ofthe flanges-38 of the column, and it is desired that the plate be ofproper length to extend from the holding members 39 at the base to theunder side of the beam f connection 40. This plate is made of the"proper length plus the necessary contraction. The first operation inapplying the plates is to weld one end thereof to each flange as shownat 41. then the plate may be chilled to contract it to the proper lengthor it may be buckled outwardly by wedges 42 to bring it to its propereffective length. It is then welded to its flange at its opposite end.If it is chilled before welding it is welded at this end whilechilled.If chilled after it is buckled outwardly it is welded at one end beforebuckling and then chilled so as to lie in contact with the flange of thecolumn throughout the entire length of the plate. Whether chilled beforeor after welding the portion of the plate between the welds is clampedto the flanges by suitable clamps such as those shown in Figs. 1 to 7 orthe clamps shown in Figs. 14 and 18, which may comprise a yoke 44 toengage under the flanges of he column and has a clamping head 45 on ascrew 46 threaded in the yoke which may be turned by any suitable toolin head 47. This clamp will press tightly against the plate or column tohold it during the welding operation. The plate is then welded to thecolumn at points between the end welds as shown at 48.

If the strengthening plates 37 are of considerable width they may bucklein the center under the compressive forces. It is, therefore, preferredto cut or punch rectangular openings 49 in the plates and weld theplates to the'column around the peripheries of these openings as shownat 50. After this welding is completed the entire opening may be filledup with the weld metal making a so-called plug weld, and thus thecenters of 1. A method of strengthening a structural member while it isunder load which comprises welding one end of a strengthening member tothe structural member, forcing the central portion of the strengtheningmember away from the structural member to reduce its effective length,welding the opposite end of the strengthening member to the othermember, chilling the strengthening member to cause it to contract so asto lie against the structural member, and welding the two memberstogether at points between the end welds.

2. .The method of strengthening a structural member having a flangeunder compression which comprises welding a metal plate at one end tosaid flange, forcing outwardly the central portion of the plate awayfrom the flange to decrease the effective length of the plate, weldingthe other end of the plate to the flange, chilling the plate to cause ittocontract and move back against the flange, and welding the plate tothe flange at points between the end welds.

3. A method of strengthening a structural member while it is underload'which comprises welding one end of a strengthening member to thestructural member, forcing the central portion of the strengtheningmember away from the structural member to reduce its effective length,welding the opposite end of the strengthening member to the othermember, chilling the strengtheningmember to cause it to contract so asto lie against the structural member, clamping the two members together,permitting the strengthening member to return to substantially thetemperature of the structural member, and then welding the two memberstogether'at points between the end welds.

' 4. The method of strengthening a .structural member having a flangeunder compression which comprises welding a metal plate at one end tosaid flange, forcing outwardly the central portion of the plate awayfrom the flange to decrease the effective length of the plate, weldingthe other end of the plate tothe flange, chilling the plate to cause itto contact and move back against the flange, clamping the plate to theflange, permitting the strengthening member to return to substantiallythe temperature of the flange, and then welding the plate to the flangeat points between the end welds. Y

5. A method of strengthening a girder or column while under load whichcomprises welding a metal strengthening member at one end to the memberto be strengthened, buckling outward the strengthening member to reduceits effective length to correspond with the stress desired for saidmember, welding the other end of said member to the member to bestrengthened, cooling the strengthening member to cause it to contractto said length,

r clamping the latter member to the girder or column, permitting itstemperature to return to normal, and then tack welding the two memberstogether between the end welds.

6. A method of strengthening a girder or column having a flange underlongitudinal compression which comprises welding a lonao gitudinallyextending metal plate at one end to said flange, buckling outwardly thecentral portion of the plate to reduce its effective length tocorrespond with the stress desired for said plate, welding theother .endof the plate to said flange, cooling the plate to cause it to contractto said length, clam-ping'the plate to the flange, permitting thetemperature of the plate to return to substantially that of the flange,and then welding the plate 40 to the flange at points between the endwelds.

7. A method of strengthening a structural member while it is undercompression comprising welding one end of a strengthening,

- member to the structural member, cooling 6 the strengthening memberbelow the temperature of the other member to shorten its length, weldingthe other'end of the strengthening member to the structural member, andwelding the two members together at points between the end welds.

8. A method of strengthening a column or 1 girder having a flange undercompressive load comprising welding one end ,of a longitudinallyextending metal plate to said flange,

its opposite ends to the structural member, at

least one of said ends being welded while the nected while thestrengthening member is shortened to an eflective length less than itsnormal length, and securing the two members together between the firsttwo connections.

11. A method of strengthening a structural member while it is under loadwhich comprises rigidly securing one end of a strengthening member tothe structural member, forcing the central portion of the strengtheningmember away from the structural member to reduce its effective length,rigidly securing the opposite end of the strengthening member to theother member, chilling the strengthening member to cause it to contractso as to lie against the structural member, and securing the memberstogether between the end connections. 12. The method of strengthening astructural member having a flange under compression which comprisesrigidly securing a metal, plate at one end to said flange, forcingoutwardly the central portion of the plate away from the flange todecrease the effective length of the plate, rigidly securing the otherend of the plate to the flange, chilling the plate to cause it tocontract and move back against the flange, and securing the plate to theflange between the end connections.

In testimony whereof I aflix my signature.

ARTHUR G. LEAKE.

: -cooling said plate below the temperature of the flange to shorten itslength to correspond withthe stress desired for said plate, welding theother end of the plate to the flange, permitting the plate to return tosubstantially the temperature of the flange, and welding the plate tothe flange at points between the end welds. I

9. A method of strengthening astructural member while it is undercompression com- 05 prising welding a strengthening member at

